This application is related to application Ser. No. 08/389,313 filed Feb. 16, 1995 by the inventor hereof that is entitled "Computer Controlled AC Circuit Breaker", that is assigned to the assignee hereof, and which is incorporated into this application by reference.
The present invention is directed generally to circuit interrupters such as switches, circuit breakers and the like for turning off an AC current, and more particularly to a circuit for interrupting a high power AC load current that has fewer components and a higher load current interrupt capability than known circuits.
Computer controlled circuit interrupters control power distribution with computers and provide various advantages over mechanical devices. For example, the over current protection is fast, energy (watt-seconds) in the circuit may be limited, operation at high temperature does not affect load current trip point, the load current is tracked accurately, and switching speed is not a function of load current. Computer controlled circuit interrupters are discussed further in the above-referenced application.
High power circuit interrupters may be needed to turn off hundreds or thousands of amperes of AC load current, and are desirably computer controlled in many applications. High power circuit interrupters of the prior art are either too slow for operation in a computer controlled circuits, are not adaptable to a solid state single integrated circuit embodiment which is desirable for computer controlled circuits, or require many components (increasing cost and complexity) to achieve modest results. For example, to turn off 500 A at 200 V with the switch discussed in the above referenced application, the switch would require eight MOS Controlled Thyristors (MCTs)--four 120 A MCTs for each polarity. In contrast, the circuit disclosed herein uses only four MCTs to turn off a 1000 A load current.
Accordingly, it is an object of the present invention to provide a novel circuit and method for interrupting an AC load current which is adaptable to computer control and obviates the problems of the prior art.
It is another object of the present invention to provide a novel circuit and method for interrupting an AC load current in which a MOS Controlled Thyristor (MCT) selectively controls transmission of the load current.
It is yet another object of the present invention to provide a novel circuit and method for interrupting an AC load current in which a pulse resonant commutation (PRC) current decreases the current through a load current controlling MCT so that even large load currents may be turned off with a single MCT.
It is still another object of the present invention to provide a novel circuit and method for interrupting an AC load current in which a PRC current for decreasing the current in a load current controlling MCT is provided from a second MCT that is turned on when the load current is to be interrupted.
It is a further object of the present invention to provide a novel circuit and method for interrupting an AC load current in which a brief PRC current for decreasing the current in a load current controlling first MCT is provided from a second MCT in a PRC circuit that is turned on when the load current is to be interrupted, and in which the load current is initially provided through a switching device in parallel with the first MCT when the first MCT is turned off, and then through the second MCT.
It is yet a further object of the present invention to provide a novel circuit and method for interrupting an AC load current in which PRC currents are provided to each of two serially connected MCTs for turning off the load current by decreasing the current through the two MCTs to an MCT "off" condition so that they may be turned off.